Texture and lattice strain evolution during tensile loading of Mg–Zn alloys measured by synchrotron diffraction

To explore the effect of neodymium (Nd) on the deformation mechanisms of Mg–Zn alloys, texture and lattice strain developments of hot-rolled Mg–Zn (Z1) and Mg–Zn–Nd (ZN10) alloys were investigated using in situ synchrotron diffraction and compared with elasto-viscoplastic self-consistent simulation under tensile loading. The Nd-containing ZN10 alloys show much weaker texture after hot rolling than the Nd-free Z1 alloy. To investigate the influence of the initial texture on the texture and lattice strain evolution, the tensile tests were carried out in the rolling and transverse direction. During tension, the {002} texture components develop fast in Z1, which was not seen for ZN10. On the other hand, fiber // loading direction (LD) developed in both alloys, although it was faster in ZN10 than in Z1. Lattice strain investigation showed that // LD-oriented grains experienced plastic deformation first during tension, which can be related to basal slip activity. This was more apparent for ZN10 than for Z1. The simulation results show that the prismatic slip plays a vital role in the plastic deformation of Z1 directly from the beginning. In contrast, ZN10 plastic deformation starts with dominant basal slip but during deformation prismatic slip becomes increasingly important

Microstructure–Mechanical Properties and Application of Magnesium Alloys

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Influence of third alloying element on dislocation slip and twinning activities in Mg-Nd-based alloys

In the present study, the influence of Zn or Al addition as a third alloying element on the deformation mechanisms of Mg–Nd-based alloys was investigated by quasi in situ tensile tests. Distinct mechanical behaviors were observed between Mg–1.0 Zn–1.7 Nd (ZN12, in wt.%) and Mg–1.0 Al–1.7 Nd (AN12) alloys. The ZN12 alloy showed a lower yield strength and higher fracture strain compared to the AN12 sample. A considerable number of slip traces, corresponding to basal and non-basal dislocations, were formed at the early deformation stage of the ZN12 sample. On the contrary, only a few grains in the AN12 sample showed obvious slip traces. To minimize the effect of grain size and texture on the activation of deformation modes, the grains were categorized into several groups based on their grain sizes and Schmid factors. By comparing the grains in the same group, it was found that basal and non-basal slip are preferred in the ZN12 sample compared to the AN12 sample. High activity of tensile twinning was observed in both samples. However, half of the twins were activated after yielding in the ZN12 sample, while a majority of the twins were formed at a higher strain in the AN12 sample.</p

Solute drag-controlled grain growth in magnesium investigated by quasi in-situ orientation mapping and level-set simulations

Critical properties of metallic materials, such as the yield stress, corrosion resistance and ductility depend on the microstructure and its grain size and size distribution. Solute atoms that favorably segregate to grain boundaries produce a pinning atmosphere that exerts a drag pressure on the boundary motion, which strongly affects the grain growth behavior during annealing. In the current work, the characteristics of grain growth in an annealed Mg-1 wt.%Mn-1 wt.%Nd magnesium alloy were investigated by advanced experimental and modeling techniques. Systematic quasi in-situ orientation mappings with a scanning electron microscope were performed to track the evolution of local and global microstructural characteristics as a function of annealing time. Solute segregation at targeted grain boundaries was measured using three-dimensional atom probe tomography. Level-set computer simulations were carried with different setups of driving forces to explore their contribution to the microstructure development with and without solute drag. The results showed that the favorable growth advantage for some grains leading to a transient stage of abnormal grain growth is controlled by several drivers with varying importance at different stages of annealing. For longer annealing times, residual dislocation density gradients between large and smaller grains are no longer important, which leads to microstructure stability due to predominant solute drag. Local fluctuations in residual dislocation energy and solute concentration near grain boundaries cause different boundary segments to migrate at different rates, which affects the average growth rate of large grains and their evolved shape

Observation of non-basal slip in Mg-Y by in situ three-dimensional X-ray diffraction

Mg-5wt%Y extruded alloy showed excellent tensile ductility along the extrusion direction. An in situ tensile test with three-dimensional X-ray diffraction (3DXRD) identified prismatic, basal, and pyramidal slip in different grains during deformation based on the analysis of grain rotation. Ex situ slip trace analysis using electron backscatter diffraction confirms the extensive activation of non-basal slip systems, which can explain the high ductility of this material. Critical resolved shear stress (CRSS) ratios between non-basal slip and basal slip are estimated from Schmid factor analysis